Direct esterification method



United States Patent 3,425,995 DIRECT ESTERIFICATION METHOD Mary E. Carter, Philadelphia, and John A. Price, Swarthmore, Pa., assignors t0 FMC Corporation,

3,425,995 Patented Feb. 4, 1959 ice vention is carried out with the molecular ratio of glycol to acid of from about 1:1 to about 15: l, but preferably from about 1.2:1 to 2.5: 1. The esterification reaction temperature ranges from about 220 to about. 290 C. and the erties of the resulting polyester.

In general, the direct esterification stage of this in- Philadelphia, Pa a corporation of Delaware 5 reaction is carried out the absence of an oxygen con- N Drawing Filed Aug 2 1966 s No. 575,242 tam ng gas at atmospheric or elevated pressure. The cat- U.S, C], 260 75 6 Cl i alytic amount of phenolate present during the esterifica- Iut.Cl.C08g 17/08 tion reaction generally ranges from about 5X10 to about 5 10 mole per mole of terephthalic acid. 10 d When the direct esterification stage is complete, as inicated, for example, by the collection of clear distillate, ABSTRACT OF THE DISCLOSURE any remaining glycol is distilled off and a polycondensa- Pro e f preparing l th l hth l tion catalyst is added to the product and condensation prising carrying out a direct esterification reaction beis Continued Under c tween terephthalic acid and ethylene glycol in the pres- Conventional polycondensation catalysts include, for ence of a phenolate which is an alkali metal or an example, antimony trioxide, antimony pentoxide, antialkaline earth metal salt of phenol to form a prepolymer mony trisulfide, antimony trifluoride, antimony triphenyl, and then polycondensin the aid prepolymer in the zinc acetylacetonate, lead oxide, sodiumalcoholate, lithipresence of a polycondensation catalyst. um hydride, zinc acetate, ferric acetate, titanium oxide, organo-tin compounds, organo-magnesium halides, and

the like. These compounds may be added at the comple- This invention relates to a method of preparing filation of the esterification reaction or before. They are ment-forming polyesters. More particularly, it relates to g n ra ly employed in amounts ranging from about the preparation of polyethylene terephthalate resin hav- 0.005 to about 0.5% based on the Weight of the reacing excellent filament-forming properties. tants. The condensation reaction is usually carried out at The manufacture of polyester resin by polycondensaa reduced pressure of from about 0.1 to 20 mm. of mertion of the product formed by the direct esterification of Our Y and a temperature of from about 230 to 320 C. in a dicarboxylic acid and a diol, is well-known. In the an inert atmosphere. case of polyethylene terephthalate, the direct esterifica- The Process of this invention y be Carried 01111 either tion procedure has not been generally accepted for the Co t nuously or batch-Wise. commercial preparation of the polymer because of the The following example is set forth to demonstrate this difiiculty, when using it, in preparing a satisfactory melt invention. spinnable resin. The polyethylene terephthalate resin Example should have a carboxyl content value of below 50 equivalents per million grams (eq./10 gr. or meq./kg.), a A mixture containing 84 g. (0.5 mole) of terephthalic minimum birefringent melting point of 258 C., and an acid, 62 g. (1.0 mole) of ethylene glycol, and 0.0113 g. intrinsic viscosity of greater than 0.60. Each of these (5 10 mole) of an alkali metal or alkaline earth metal resin characteristic requirements is necessary to provide phenolate was charged to a Fischer-Porter pressure asa material which can be melt extruded to form filaments sembly equipped with a nitrogen sparge tube and a disand fibers which can be processed to form substantially tilling arm. The reactor was lowered into an oil bath colorless, stable, high tenacity textile products. maintained at 260 C. and flushed for 10 minutes with Furthermore, from a commercial standpoint, it is dedry nitrogen. A nitrogen pressure of 60 psi. was applied sirable to produce polyester resin having acceptable propand a distillate of water-ethylene glycol was collected. erties in the process which takes the shortest possible time When a clear liquid, i.e., solution, was obtained, the to complete, pressure was reduced to atmospheric and the remaining It is an object of the present invention to prepare polyexcess glycol was distilled. The low molecular weight ethylene terephthalate resin suitable for melt extrusion polymer (prepolymer) was further reacted in the presinto non-degraded, processable filaments by a direct esterence of a condensation catalyst, e.g., antimony trioxide ification and polycondensation procedure. or antimony trisulfide, to a high molecular weight poly- This and other objects are accomplished in accordance ester undef Vacuum for {our hollrs at The P 3- with this invention which concerns a method of preparing condellsatlon catalyst concentration was 034% based on filament-forming polyethylene terephthalate wherein terthe welght of the Prepolymerephthalic acid and ethylene glycol are directly esteriiied The following table sets forth conditions and results of and the product of esterification is polycondensed in the various reactions carried out as described above.

TABLE Esterifica- Prepolymer Polumer Esterification Additive tion Time, Carboxyl Condensation Intrinsic Melting Oarboxyl Hrs.:Mins. Content, Catalyst Viscosity Pt.,0. Content,

meg/kg. meq./kg

None 3:40 316 0. 36 261 82 Do- 3 :40 316 0.80 250 40 Calcium Phenolate 2:30 125 0. 99 260 37 0. 93 262 27 Sodium Phenolate 2 15 180 0. 262 41 presence of a condensation catalyst, the improvement The above table indicates that the phenolates of alkali comprising carrying out the direct esterification step in metals and alkaline earth metals when used as esterificathe presence of an alkali metal or alkaline earth metal tion catalysts consistently produce better polymers in acphenolate in an amount sufiicient to improve the propcordance with this invention, than reactions wherein no esterification catalyst is used. Furthermore, in general, the use of the additive cuts esterification time considerably and produces prepolymers which are more highly esterified. The esterification additive provides a prepolymer which may be polycondensed to a high molecular weight, low diethylene glycol content polymer, as indicated by its high intrinsic viscosity and melting point.

The testing used to determine the above resin characteristics were uniformly carried out using conventional procedures.

Various changes and modifications may be made practicing the invention without departing from the spirit and scope thereof and, therefore, the invention is not to be limited except as defined in the appended claims.

We claim:

1. A method for preparing filament-forming polyethylene terephthalate wherein terephthalic acid and ethylene glycol are directly esterified and the product of esterification is condensed in the presence of a condensation catalyst, the improvement comprising carrying out the direct esterification reaction in the presence of a catalytic amount of a phenolate esterification additive which is an alkali metal or alkaline earth metal salt of phenol.

2. The method of claim 1 wherein the phenolate is present in an amount ranging from about 5X10" to about 5X10" mole per mole of terephthalic acid.

3. The method of claim 1 wherein the esterification reaction is carried out in the presence of an alkali metal phenolate.

4. The method of claim 3 wherein the alkali metal is sodium.

5. The method of claim 1 wherein the esterification reaction is carried out in the presence of an alkaline earth metal phenolate.

6. The method of claim 5 wherein the alkaline earth metal is calcium.

References Cited UNITED STATES PATENTS 3,056,818 10/1962 Werber 260-75 XR 3,326,965 6/1967 Schultheis et a1. 260-475 3,329,651 7/1967 Dobinson 26075 WILLIAM H. SHORT, Primary Examiner.

LOUISE P. QUAST, Assistant Examiner.

US. Cl. X.R. 

